A broad object of the invention is a compact dental handpiece or prophylaxis angle that minimizes the passage of material such as abrasives from the open or tool-receiving end to the rotating parts and closed end.
Other dental handpieces are shown in Richmond U.S. Pat. No. 3,436,830 and Bailey U.S. Pat. No. 4,014,099, and the art cited in them. Prior art has suggested the disposition of the driven gear toward the closed end of the cross head, as witness Fernald U.S. Pat. No. 1,170,523 and Heatherington U.S. Pat. No. 3,978,586. Fernald has two shaft bearings that must be aligned, and does not have any thrust bearing arrangement. Heatherington has only a sketchy showing and merely suggests location of the driven gear at the closed end of the head bore. Cooper U.S. Pat. No. 2,469,261 purports to illustrate an arrangement by which a rubber cup can seal by compression, but the disclosure is of an arrangement different from the one here proposed in that, among other things, the driving mechanism between the shaft and the rubber cup is part of the same mechanism that is supposed to give the sealing arrangement.
Objects of the present invention therefore include broadly the arrangement of the cross head for a dental handpiece that minimizes the possibility of having granular or abrasive material reach the moving parts where it could abrade them. The objects also include the provision of a single cylindrical bearing for the driven shaft that has a close fit with the shaft and a long path between its ends, to make a difficult path for the abrasive or liquid materials between the open and closed ends of the head. Also the single long bearing provides a very stable high-speed shaft, and does not require the alignment of multiple bearings to support the shaft. It will prevent irregular rotary motion of the shaft and of the dental instrument attached to it.
Another object of the present invention is to provide a cross head for a dental handpiece wherein the end thrust applied to the dental instrument is taken by the bearing of the driven shaft against a fixed cap at the closed end of the cross head and particularly where it is taken by the back face of the driven gear.
Further objects include the construction of a dental handpiece with a minimum number of parts.